El Niño is the warming phase of the El Niño–Southern Oscillation (ENSO), a global climate phenomenon driven by variations in sea surface temperatures and atmospheric pressure over the tropical Pacific Ocean. During El Niño events, sea surface temperatures warm across the tropical Pacific, accompanied by higher than normal sea level air pressure over Indonesia, Australia, and regions extending across the Indian and Atlantic Oceans.

These atmospheric changes disrupt typical weather patterns across the tropics and subtropics. In regions such as Southeast Asia, higher air pressure is associated with prolonged dry seasons, reduced rainfall, and water shortages. In countries like Indonesia, these drier conditions can intensify seasonal fire risks and exacerbate wildfires, contributing to regional problems such as transboundary haze.

El Niño events typically recur every two to seven years and generally last about one year, alternating with neutral periods or La Niña, the cooling phase of ENSO. Particularly severe instances, known as Super El Niño or very strong El Niño events, occur when average sea surface temperatures in parts of the Pacific rise by 2°C or more, significantly increasing the likelihood of widespread droughts, food shortages, severe flooding, and heightened wildfire activity globally.